Cross raceway lapping of ball bearings

ABSTRACT

A METHOD AND APPARATUS FOR RANDOMLY LAPPING A BALL BEARING RACE AND REMOVING THE DEVIATIONS FROM A SMOOTH CROSS RACE CURVATURE WHEREIN THE BEARING RACE IS ROTATED ABOUT ITS NOMINAL CENTER, A CONFORMING BALL IN A SLURRY OF FINE ABRASIVES IS ROTATED IN A HIGHLY RANDOM MANNER IN THE RACE THUS TRANSFERRING THE UNIFORM RADIUS AND FINISH OF THE BALL TO THE BEARING RACE SURFACE.

P 1971 J. F. ROBINSON 3,608,244

CROSS RACEWAY LAPPING 0F BALL BEARINGS Filed July 22, 1968 FIGJ FIG 2ROTATING MEANS INVENTUR. JOHN F. RQBINSON ATTORNEY Patented Sept. 28,1971 3,608,244 CROSS RACEWAY LAPPING F BALL BEARINGS John F. Robinson,Newport Beach, Calif., assignor to North American Rockwell CorporationFiled July 22, 1968, Ser. No. 746,575 Int. Cl. B24b /16 US. Cl. 51105R 5Claims ABSTRACT OF THE DISCLOSURE A method and apparatus for randomlylapping a ball bearing race and removing the deviations from a smoothcross race curavture wherein the bearing race is rotated about itsnominal center, a conforming ball in a slurry of fine abrasives isrotated in a highly random manner in the race thus transferring theuniform radius and finish of the'ball to the bearing race surface.

BACKGROUND OF THE INVENTION (1) Field of the invention The presentinvention relates to an apparatus for finishing bearing raceways, andmore particularly, to an apparatus for randomly lapping a ball bearingraceway surface with a conforming lapping ball.

(2) Description of the prior art In precision ball bearings Where lowrunning friction and long life are required, the surface condition ofthe raceway is of prime importance.

The present methods of finishing raceways are to control the cross-racecurvature as closely as possible with either a form cut or a form grind,then polish the surface to a very fine finish. The shape of the cuttingtool or grinding wheel is initially designed to conform to the nominalradius of the desired raceway. Cutting tools and grinding wheels,however, leave much to be desired. Since no tools or polished wheelswill maintain uniform geometry while cutting or polishing, thecross-section of the bearing race will display irregularities. At amicroscopic level the bearing surface will display both waviness andcircular scratch marks. The waviness is due to changes from a trueradius as the form cutter or grinder breaks down. The scratch marks aredue to the polishing operation. The polishing tends to follow thegeometry established by the forming operation.

Another technique resorted to, which is capable of furnishing somewhatbetter results, involves running a full complement of balls in a slurryof fine abrasives in a ball bearing system. The halls, however, tend togo into planetary motion, that is, they tend to rotate about a givenfixed axis. This results in the race irregularities actually cuttinginto the balls such that the contour gen erated averages between theball and the race contour leaving the raceway surface with a substantialnumber of remaining irregularities.

In a normal ball bearing, operating at rotational speeds suflicient togenerate a hydrodynamic film, the onset of wear depends upon thethickness of the hydrodynamic film in relation to the number and heightof the surafce irregularities. Where the asperities exceed thehydrodynamic film thickness, wear takes place. Conventional ballbearings start to wear initially by breaking down the peaks of thelargest asperities. As these high points are broken down, wear debrisbegins to accumulate in the lubricant contributing to further wear.

The next stage of wear takes the form of surface fatigue where the peaksof some of the larger asperities have been removed. With repeatedcycling, these highly stressed localized fatigue conditions force smallparticles to break 01?, according to classical fatigue theory. Thisprocess is degenerative since more asperities are exposed, generatingmore debris until lubrication and/ or bearing failure takes place.

SUMMARY OF THE INVENTION According to the present invention, these andother problems of the prior art are eliminated by substantially reducingthe number and magnitude of raceway surface irregularities. This isachieved by utilizing a lapping ball conforming to the racewaycurvature. The bearing race is rotated about its nominal center. Theconforming ball is rotated in a highly random manner, sometimes acrossthe raceway, sometimes in and sometimes contra to the direction ofrotation, sometimes at various angles to all of these directions. Theaddition of a slurry of fine abrasives provides all necessary cuttingaction.

The advantages of such a procedure are many. The uniform radius andfinish of the lapping ball is transferred to the bearing raceway. Theirregularities in the raceway surface are substantially eliminated thusretarding the onset of wear and greatly increasing bearing life.

It is, therefore, an object of the present invention to provide a novelmeans for finishing ball bearing raceway surfaces.

It is a further object of the present invention to provide a novel meansfor eliminating irregularities in the surface of a ball bearing raceway.

It is a still further object of the present invention to provide a meansfor randomly lapping ball bearing raceway surfaces to a very finefinish.

It is another object of the present invention to improve the basicgeometry and finish of ball bearing raceways so as to increase bearinglife.

Still other objects, features, and attendant advantages of the presentinvention will become apparent to those skilled in the art from areading of the following detailed description of the preferredembodiments constructed in accordance therewith, taken in conjunctionwith the accompanying drawings wherein like numerals designate likeparts in the several figures.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-section of a bearingrace illustrating the microscopic irregularities left in the racesurface by standard finishing techniques.

FIG. 2 is a cross-section of a bearing race and ball illustrating thecondition of the raceway after a ball has worn down the peaks of some ofthe larger irregularities.

FIG. 3 is a diagram of the method and means for finishing racewaysurfaces in accordance with the teachings of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawingsand, more particularly, to FIG. 1 thereof, there is shown across-sectional view of a bearing race 10 finished in accordance withprior art techniques wherein surface irregularities 11 are shown inexaggerated perspective for clarity. The cross-section illustrates bothwaviness, which represents deviations from a true radius caused by theform cutter or grinder breaking down, and finer scratch deviations,generally following the geometry established by the forming operation,caused by the polishing techniques. The high points of theseirregularities will establish contact first with the bearing ball. Theball will, therefore, tends to distribute its entire load on thesecontact points.

Conventional ball bearings start wear initially by breaking down thehigh points of these sharp irregularities as illustrated in FIG. 2. Asthe high points are broken down, wear debris begins to accumulate in thelubricant contributing to further wear, as previously discussed. Thenext stage of wear takes the form of surface fatigue where the,asperities have been removed. With repeated cycling, these high stress,localized fatigue conditions cause small particles to break olf,according to classical fatigue theory. This process is degenerativesince more asperities are exposed, generating more debris untillubrication and/ or bearing failure takes place.

Referring now to FIG. 3, according to the present invention, theseproblems are significantly reduced by the raceway lapping method andmeans disclosed which substantially eliminates the racewayirregularities. Bearing race 20 is rotated about its nominal center 25.A conforming lapping ball 21 whose radius of curvatures conforms to theradius of the race, is slowly rotated in a highly random manner,sometimes across the race, sometimes in and sometimes contra to thedirection of rotation, sometimes at an angle to each of the abovementioned directions. Complete randomness of rotation is not required solong as the axis of rotation changes in a non-reptitive manner for asubstantial time period. It is normally desirable to fabricate thelapping ball from a material softer than the race material so thatabrasives will adhere to the softer material rather than the surfacebeing removed. Otherwise, the abrasives may tend to be charged into therace surface, deleteriously affecting the polished surface. Pressure onand random rotation of the ball is affected by paddle 22. Retainer 23losely holds the ball and prevents it from falling out of the race. Aslurry of abrasives introduced into the area between the ball and therace provides all necessary cutting action, The random rotation of thelapping ball substantially eliminates all raceway irregularities andinsures that the uniform radius and finish of the ball is transferred tothe bearing race. Although the lapping operation has been illustratedwith reference to an inner raceway, it is contemplated that outerraceways will be lapped in the same manner.

The result is a uniform raceway surface which exhibits a substantiallymore uniform cross-sectional geometry. Raceway surfaces finished in thismanner exhibit a reduction in breakway friction of as much as 50%, thussubstantially reducing the friction level of the ball bearing andincreasing bearing life.

In one lapping operation, a slurry consisting of two parts by weightjewelers rouge and one part by weight of tricresophosphate was usedalthough the specific slurry composition is not critical. The races,both inner and outer, were held in a jewelers lathe and rotated atapproximately 100 r.p.m.s. The ball used for lapping was made of 440 Chardened to 40-50 R. with its diameter substantially in conformance withthe race to be lapped. A load of approximately 2. ounces was applied tothe ball. The result was a bearing race exhibiting a significantlysmoother surface than that obtainable by any other prior art procedure.

The advantages of the present lapping procedure and means may now beappreciated. A smoother more regular bearing raceway surface is achievedexhibiting a significantly lower breakway torque resulting in lowerrunning friction and increased bearing life.

While the invention has been described with respect to several physicalembodiments constructed in accordance therewith, it will be apparent tothose skilled in the art that various modifications and improvements maybe made without departing from the scope and spirit of the invention.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrative embodiments, but only the scope ofthe appended claims.

I claim:

1. An apparatus for randomly lapping the raceway surfaces of a bearingrace of a ball bearing comprising a lapping ball having a uniform radiusof curvature defining a smooth and uniform surface of said ball, meansto rotate said bearing race about its nominal axis, means for looselyretaining said ball the close proximity to said raceway surface whilesaid bearing race is rotated, means for introducing a slurry ofabrasives onto said raceway surface, means for imparting complete randommotion to said ball in said race, and means for selectively applyingpressure to said ball whereby the uniform radius of curvature of saidball is imparted to said raceway surface eliminating racewayirregularities.

2. An apparatus according to claim 1 wherein the radius of curvature ofsaid ball substantially conforms to the nominal radius of said bearingrace.

3. An apparatus according to claim 2 wherein said ball is of a materialsofter than the material comprising said raceway surface, whereby saidabrasives introduced onto said raceway surface will tend to adhere tosaid ball. 7

4. An apparatus according to claim 1 wherein said abrasive is a fineabrasive and is introduced onto said raceway surface between said balland said surface and said bearing race is slowly, rotated.

5. An apparatus for randomly lapping the raceway surfaces of a bearingrace of a ball bearing comprising a single lapping ball having a uniformradius of curvature defining a smooth and uniform surface of said ball,means to slowly rotate said bearing race about its nominal axis, aretainer operatively connected to said apparatus to loosely hold saidball in close proximity to the raceway surface while said bearing raceis slowly rotated, means for introducing a slurry of a fine abrasiveonto said raceway surface, a paddle operatively connected to saidapparatus for imparting complete random motion to said ball and toselectively apply pressure to said ball, whereby the uniform radius ofcurvature of said ball is imparted to said raceway surface eliminatingraceway irregularities.

References Cited UNITED STATES PATENTS '634,452 10/1899 Gennert 51-1051,352,790 9/ 1. 920 Danielsson 51-105 1,666,713 4/1928 Maynard 512631,708,491 4/1929 Alden 5126X 2,073,216 3/1937 Mancuso 5126X 2,356,4998/1944 Beduneau 51--105 LESTER M. SWINGLE, Primary Examiner US. Cl. X.R.51 91 Q22 3? UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent No. 3 6Q8 244 Dated Segtember 28, 1971 Inventor 5) JOHN FROBINSON It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below;

Column 1, line 39, change "polished" to read "polishing" Column 4,lineS, after "only" insert --by--;

line 13, change "the" to read "in".

Signed and sealed this 11 th day of March 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Commissioner of PatentsAttesting Officer

